The ARID Family Transcription Factor Bright Is Required for both Hematopoietic Stem Cell and B Lineage Development

Abstract

Bright/Arid3a has been characterized both as an activator of immunoglobulin heavy-chain transcription and as a proto-oncogene. Although Bright expression is highly B lineage stage restricted in adult mice, its expression in the earliest identifiable hematopoietic stem cell (HSC) population suggests that Bright might have additional functions. We showed that >99% of Bright ؊/؊ embryos die at midgestation from failed hematopoiesis. Bright ؊/؊ embryonic day 12.5 (E12.5) fetal livers showed an increase in the expression of immature markers. Colony-forming assays indicated that the hematopoietic potential of Bright ؊/؊ mice is markedly reduced. Rare survivors of lethality, which were not compensated by the closely related paralogue Bright-derived protein (Bdp)/Arid3b, suffered HSC deficits in their bone marrow as well as B lineage-intrinsic developmental and functional deficiencies in their peripheries. These include a reduction in a natural antibody, B-1 responses to phosphocholine, and selective T-dependent impairment of IgG1 class switching. Our results place Bright/Arid3a on a select list of transcriptional regulators required to program both HSC and lineage-specific differentiation.The formation and maintenance of blood throughout fetal and adult life rely on the self-renewal of hematopoietic stem cells (HSCs). Rare HSCs arise in the embryonic yolk sac and aorta-gonad mesonephros AGM, seed the fetal liver, and then circulate in the bone marrow of adult mammals. Fetal and adult HSC progenitors become progressively dedicated to differentiation into erythrocytes, myeloid cells, and lymphocytes. Transcription factors critical for the specification and formation of HSCs cover a wide range of DNA binding protein families. An emerging theme is that many of these same regulators are required later for the differentiation of individual blood lineages, which explains why a number of HSC transcription factors were discovered and originally characterized because of their deregulation in hematopoietic malignancies.Bright/Arid3a/Dril1 is the founder of the AT-rich interaction domain (ARID) superfamily of DNA binding proteins (18,60). Bright, in a complex with Bruton's tyrosine kinase (Btk) and TFII-I, binds to specific AT-rich motifs within the nuclearmatrix attachment regions (MARs) of the immunoglobulin heavy-chain (IgH) intronic enhancer (E) and selected IgH promoters to activate IgH transcription (18,25,30,43,44,55,57,58). B cell-specific, transgenic overexpression of Bright leads to partial blocks at both the late-pre-B and T1 immature stages, skewed marginal-zone (MZ) B cell development, increased natural IgM antibody production, and intrinsic autoimmunity (49). Transgenic dominant negative (DN) inhibition of Bright DNA binding results in reduced levels of IgM in serum and functional perturbation of IgM secretion by B-1 cells (39,48). A small pool of Bright cycles from the nucleus into plasma membrane lipid rafts, where it associates with Btk to dampen antigen receptor signaling (48).While highly B lineage restricted in...

Arid3a is essential to execution of the first cell fate decision via direct embryonic and extraembryonic transcriptional regulation

“…Arid3a, the founding member of the ARID family of TFs, has been characterized as a transactivator of both B lymphocyte development and cell cycle progression (Herrscher et al 1995). Loss-of-function studies revealed that >98% of Arid3a À/À mice die prior to embryonic day 11.5 (E11.5) (Webb et al 2011), suggesting a potential role in embryonic development. A recent follow-up study showed that singular loss of Arid3a is sufficient for reprogramming as well as enhancement of standard four-factor reprogramming of mouse embryonic fibroblasts (MEFs) to fully induced pluripotent stem cells (Takahashi and Yamanaka 2006;Popowski et al 2014).…”

Interferon-α signaling promotes embryonic HSC maturation

“…We picked Arid3a as a candidate because of its known role in FL HSCs, which are exposed to higher levels of IFN-a ( Figure 1F). 40 Examination of Arid3a protein levels in E11.5 embryonic tissues indicated that, in addition to the FL, Arid3a is expressed at sites of embryonic hematopoiesis, including the AGM, yolk sac, and placenta ( Figure 5B). 40 To determine whether Arid3a is expressed in endothelial or hematopoietic cells, we stained the AGM with CD45 and VEcadherin, and sorted by flow cytometry into the four fractions (supplemental Figure 3A- Figure 5C).…”

“…40 They also have FL HSC defects, 40 but whether they are impaired in AGM hematopoiesis is unknown. We first determined whether hematopoietic progenitors are present in the Arid3a KO AGM by immunostaining for Runx1 (supplemental Figure 3F-G).…”

Lin28B/Let-7 Regulates Expression of Oct4 and Sox2 and Reprograms Oral Squamous Cell Carcinoma Cells to a Stem-like State

“…3A). ARID3B is a DNA-binding protein belonging to the AT-rich interactive domain (ARID) family of transcriptions factors that are involved in diverse biologic processes (30), and HMGA2 is a member of the highmobility group AT-hook protein family and has been reported to be a Let7 target (8) and directly binds to Sox2 promoter in glioblastoma cells to induce Sox2 expression (26). To validate the bioinformatics data, we established a panel of patient samplederived CD44 À ALDH1 À OSCC cells with different combination of overexpressed Lin28B, Let7, and Spg-Let7.…”